The present invention is directed to electric relays and, more specifically, to bistable electromagnetic systems for relays.
A bistable electromagnetic system for relays is disclosed, for example, by EP 0 686 989 A1. In the bistable switch mechanism therein, a part cross-section of the magnetic circuit is formed by the permanent magnet. This is realized such that the permanent magnet is inserted between the two parts of a two-part yoke and is correspondingly polarized in longitudinal yoke direction, whereby the rest of the cross-section is fashioned either as air gap or is filled to a greater or lesser extent by a ferromagnetic section. As a result of the two yoke parts joined to one another in longitudinal direction together with the additional permanent magnet, a tolerance summing derives for the length of the yoke, and additional fabrication outlay is required in order to bring one pole face at the end of the yoke into a common plane with a pole face at the end of the core. Said publication, however, also proposes an embodiment wherein a one-piece yoke with a lateral incision or slot is to be provided for the acceptance of the permanent magnet. In this case, the overall length of the yoke is not subject to any tolerance summing. However, the fitting of the permanent magnet into such an incision requires substantial outlay if a reproduceable coupling between the permanent magnet and the adjoining yoke parts is to be assured.
Accordingly, there is a need for an improved bistable electromagnetic system for relays which is easier and therefore less costly to manufacture.